Fracture healing consists of the local activation of the resting potential for osteogenesis at the fracture site. Direct current in the low microamperage range is a potent stimulus to osteogenesis locally in intact bones in several animal species. This stimulation of osteogenesis has been shown to accelerate fracture healing in the fibula of the rabbit. Seven cases of established nonunion of fractures in man have united after further immobilization and the application of direct current to the non-union site. Systematic study of the ability of direct current to accelerate the rate of fracture healing and to augment the capacity for fracture healing requires standard experimental models. We have devised canine fracture healing models for both healing rate and healing capacity, and have developed reproducible end points for assessment of fracture healing, involving roentgen evaluation, histologic assessment and biomechanical testing. We will study the influence of three different types of direct current generators on fracture healing in the dog. This study will also evaluate electroneutral bone plates for use in association with direct current generators and will examine the optimum characteristics for electrode design and placement. The objective is to define the optimum conditions for stimulation of fracture healing by direct current. In view of the estimated 2,050,000 fractures and 100,000 cases of nonunion of fractures annually in the United States alone, the potential importance of the work is clear.